1. Field of the Invention
The present invention relates to a driving method of an AC type plasma display panel, referred to hereinafter as a PDP, of a matrix formation having electrode pairs to determine surface discharge cells.
2. Description of the Related Arts
A surface discharge type PDP is suitable particularly for colored displays using fluorescent materials, among the AC driven PDPs where the wall charge is utilized for selective lighting. There is interest in such displays as a large screen display device for high-definition television.
FIG. 1 is a plan view schematically illustrating the electrode structure of a surface discharge type PDP 10. FIG. 2 schematically illustrates a decomposition perspective view, where are shown an internal structure of the surface discharge type PDP 10.
PDP 10 illustrated therein has plural electrode pairs 12 each of which consist of first and second sustain electrodes X & Y extending straight and mutually in parallel, and plural straight address electrodes A orthogonal to the first and second plural sustain electrodes X & Y. where each electrode pair 12 corresponds to a single line L, and each address electrode A corresponds to a single row, each of the display matrix.
That is, the electrode structure of a display cell C, i.e. a display element, of PDP 10 is of a three-electrode structure where electrode pair 12 intersects with address electrodes A.
Usually, first sustain electrodes X are commonly connected with each other for simplification of the driving circuit.
On the other hand, second sustain electrodes Y are independent as an individual electrode for each line L in order to enable line-sequential screen scanning.
As shown In FIG. 2, PDP 10 is composed of a first glass substrate 11 placed on the front side, first and second sustain electrodes X & Y thereon, a dielectric layer 17 thereon for the AC drive, a protection film 18 formed of magnesium oxide, referred to hereinafter as MgO, a second glass substrate 21 on the back side, address electrodes A thereon, separator walls 29 each straight in a plane on the second glass substrate 21 when looking down, and fluorescent layers 28 for the full color display, etc.
Discharge space 30 between the two glass substrates 11 and 21 is divided along the line direction, i.e. the direction along which the first and second sustain electrodes X & Y are extending, by separator walls 29 into each sub-pixel EU, whereby the gap size between two glass substrates 11 & 21 is also determined.
First and second sustain electrodes X & Y are arranged on the inner surface of first glass substrate 11. Each of sustain electrodes X & Y is composed of a wide transparent conductive film 41 and a metal film 42 thereon for securing its electrical conductivity.
Transparent conductive film 41 is patterned as a belt shape wider than metal film 42 so that the surface discharge may expand.
In order to reduce ion bombardment caused from the surface discharge, fluorescent layer 28 is located away from sustain electrodes X & Y, between each separator wall 29 on second glass substrate 21. Fluorescent layer 28 is locally excited by the ultraviolet rays generated in the surface discharge, so as to emit light.
Among the visible radiations emitted from the surface of fluorescent layer 28, i.e. the surface to face the discharge space, the light which can penetrate through glass substrate 11 becomes a display light.
Pixel, i.e. picture element, EG of the screen matrix consists of three sub-pixels EU which line up along the line direction, where the lighting colors of the three sub-pixels EU are mutually different as denoted with R, G and B, so that each displayed color of a single pixel is determined by the combination of the basic R, G, and B. Each subpixel is formed of the display cell C and an address cell which is not drawn in the figure, but is located at the intersection of address electrode A and second sustain electrode Y.
The pattern arrangement of separator walls 29 is called a stripe pattern, where the part which corresponds to each row in discharge space 30 extends in the row direction continuously to cross over all the lines. The emitting color of sub-pixels EU in each row is identical.
Second sustain electrode Y of the electrode pair 12 and address electrode A are used for selecting, i.e. addressing, a pixel EU to light or not to light. That is, a screen scanning is performed sequentially line by line by applying a scan pulse onto sequential ones of n sustain electrodes, where n indicates the quantity of the lines; and a predetermined electrically charged state is formed in the thus selected address cell of each row by an opposing discharge, i.e. an address discharge, generated between the second sustain electrode Y and an address electrode A selected in accordance with the contents of the display.
After the addressing operation is thus performed, upon an application of the sustain pulses of a predetermined peak value alternately onto first and second sustain electrodes X & Y, a surface discharge, i.e. sustain discharge, takes place in the display cell C in which wall charges of a predetermined amount existed at the end of the addressing operation.
FIGS. 3A and 3B schematically illustrate a prior art driving method for the reset period. FIG. 3A schematically illustrates waveforms of applied voltages to each electrode; and FIG. 3B schematically illustrates discharges in the display cell.
In the AC drive in which the wall charge is utilized, it is necessary to initialize the electrically charged states of dielectric layer 17 prior to the addressing operation, i.e. rewriting, of the screen in order to prevent an influence of the previous screen.
Therefore, a reset period is provided prior to the address period.
In the prior art driving method during reset period TR, the surface discharge, i.e. the writing discharge, was caused, as shown in FIG. 3B with solid arrows, between first and second sustain electrodes X & Y by the application of a write pulse Pw having a peak value of, for instance, 340V. The pulse Pw exceeds the surface discharge starting potential VfXY, for instance, 250-960V, onto first sustain electrode X as shown in FIG. 3A, while second sustain electrode Y is kept at zero voltage.
Moreover, in order to prevent a discharge between first sustain electrode X and address electrode A, a pulse Paw having, for instance, a peak value 110 V of the same polarity as writing pulse Pw was applied to address electrode A concurrently to the application of writing pulse Pw, where the voltage difference between first sustain electrode X and address electrode A is lower than the discharge firing voltage therebetween.
This is because, if a discharge having address electrode A as a cathode is caused between first sustain electrode X and address electrode A, as shown with an arrow drawn with a broken line in FIG. 3B, positive ions generated by the discharge collide with fluorescent layer 28, resulting in deterioration of the fluorescent material.
In this specification, the term "writing discharge" indicates a discharge compulsorily caused by an application of a driving voltage which exceeds the surface discharge firing voltage.
The wall charges are once accumulated on dielectric layer 17 by the writing discharge. However, in response to the fall of writing pulse Pw there is caused a so-called self-discharge of the wall charge whereby the wall charges on dielectric layer 17 almost disappear.
In another driving method, during reset period that voltages having mutually reversed polarities are applied concurrently to first sustain electrode X and second sustain electrode Y so that the voltage difference between first and second sustain electrodes X & Y becomes higher than surface discharge firing voltage VfXY. This method relaxes a restriction of the withstanding voltage rating of the driving circuit.
However, the driver circuit of second sustain electrodes Y, which are individual, becomes complex.
A problem in the prior art method was in that some of the wall charges were generated so excessively during the write discharge that the wall charges remained even when the self-discharge was generated thereafter, because the peak value of writing pulse Pw, i.e. a writing voltage, was set so high that the potential difference between first and second sustain electrodes X & Y would surely cause the write discharge regardless of the existence of the remaining wall charge. It is also a natural requirement that a lower writing voltage is preferable.